Effect of surface acidity and basicity of supported Ni catalysts on the N-alkylation of isopropylamine with isopropanol

The N-alkylation of amines with alkylating reagents is widely used in the synthesis of aliphatic amines, which is usually catalyzed by homogeneous catalytic systems. In this work, the heterogeneous catalysts Ni/AlSiO (NAS), Ni/LaAlSiO (NLAS) and Ni/LaO (NL) with different strengths of acidity and basicity were used in the N-alkylation of isopropylamine (IPA) with isopropanol (IPO) to diisopropylamine (DIPA) in a fixed-bed reactor, and the effect of surface acidity and basicity of the supported Ni catalysts on the N-alkylation was studied by microcalorimetric adsorption and in situ Fourier transform infrared spectra. It was found that the surface acidity and basicity of the supported Ni catalysts affected the adsorption and interaction of IPO, IPA and DIPA on the supported Ni catalysts, and IPO and IPA molecules were strongly adsorbed onto the strong acidic surface, which would improve the N-alkylation reaction. In addition, the generation of imine species from the dehydrogenation of IPA greatly decreased the activity of the N-alkylation reaction, and the strong adsorption of dissociated H from the adsorption of IPO, IPA or DIPA on acidic surface inhibited the generation of imine species, which promoted the conversion of IPA. Meanwhile, the strong adsorption of dissociated H on acidic surface also promoted the hydrogenation of diisopropylimine, which increased the selectivity to DIPA.